The present assignee has provided several systems for either lowering or raising a window covering, or for moving the slats of a window covering between open and closed positions, under control of a hand-held remote or other control device. These systems include a motor that is coupled through gears to the window covering activation mechanism. When the motor is energized in response to a user command signal, the activation mechanism moves the window covering. Such assemblies are disclosed in U.S. Pat. No. 6,433,498, incorporated herein by reference.
The present assignee has also provided systems for determining the position of the window coverings based on counting motor pulses, and for braking the motor from turning when it is not energized. By knowing the position of the window coverings, features such as automatic repositioning the window covering to a preset position can be provided. The present invention likewise provides structure and methods for braking an object in the absence of power while minimizing the effects of the brake during motor operation.
In the parent application, one or more permanent magnets are disclosed that are juxtaposed with the rotor to generate a magnetic field which interferes with the rotor slots and thereby creates an extra reluctance torque on the motor shaft. The extra reluctance torque establishes a static brake, to hold the rotor from undesirably turning under the weight of the window covering when the motor is deenergized.
While effective, the present invention recognizes that even though the braking field does not unduly affect motor operation when the motor is energized, it is possible to even further reduce brake drag on the motor when it is operating.